
“Contradiction is not a sign of falsity, nor the lack of contradiction a sign of truth.”
Source: Butcher Bird
“Contradiction is not a sign of falsity, nor the lack of contradiction a sign of truth.”
Source: Labyrinths of Reason (1988), Chapter 1: "Paradox", p. 21
“Five exclamation marks, the sure sign of an insane mind.”
Variant: Multiple exclamation marks,' he went on, shaking his head, 'are a sure sign of a diseased mind.
Source: Reaper Man
“What sign is there more plain
Than self-destruction, of a mind insane?”
Quale è di pazzia segno più espresso
Che, per altri voler, perder se stesso?
Canto XXIV, stanza 1 (tr. B. Reynolds)
Orlando Furioso (1532)
Alexander Bain, On the Study of Character, including an estimate of phrenology http://books.google.com/books?id=xLhcAAAAcAAJ&pg=PA292, 1861, p. 292.